Page:Collected Physical Papers.djvu/377

 XXVII

THE MAGNETIC CRESCOGRAPH AND THE MAGNETIC RADIOMETER

In winter the growth appears to be in a state of arrest; in reality growth may persist but its rate is too slow to be detected even by the High Magnification Crescograph in which two levers produce a compound magnification of 10,000 times. It may be thought that further magnification could be obtained by a compound system of three levers; there is, however, a limit to the number of levers that may be employed with any advantage, for the slight overweight of the last lever becomes multiplied, exerting a tension so great on the plant as to interfere with the normal rate of its growth. The friction at the bearings also becomes added up by an increase in the number of levers which obstruct the free movement of the last recording lever. Magnification requiring additional material contact between different levers have, therefore, to be abandoned and it became necessary to devise an ideal method of magnification without contact. In the device perfected for this purpose a single magnifying lever attached to a growing plant upsets a very delicately balanced magnetic system (cf. fig. 114). The indicator is the reflected spot of light from a mirror carried by the deflected magnet. I have thus been able to produce a magnification as high as 50 million times. This order of magnification would lengthen a single wave of sodium light to 2,500 cm. It is obvious